class question 2

Sorry Another question- Do instances of classes remain in 'communication' with each other if declared my different functions in a case switch statement. At present I have an admin.php which is one long swtich statement. Wihin each is a list iof functions which created the elements of the page Each of these functions are defined in anither file and are instances of classes. If I create an instance of a DB class for exapmle- can I refer to it thoughout the visit to the website- ie does it maintaoin its values and variables even if different functions freom the main index.php page are called sorry if this is really confusing any ideas much appreciated